In a typical turbine engine used in a power generating plant, incoming air is compressed, and the compressed air is then routed to a plurality of combustor assemblies which are arrayed around the periphery of the engine. In each combustor assembly, fuel is added to the compressed air, and the air-fuel mixture is ignited. The resulting expanding gases are then routed to the turbine blades to produce a rotational force.
In a typical combustor assembly for such a turbine engine, a generally cylindrical flow sleeve surrounds the outer portion of part of the assembly. A generally cylindrical combustor liner is concentrically mounted inside the flow sleeve. Air from the compressor section of the turbine engine is routed through the annular space between the exterior surface of the combustor liner and the interior surface of the flow sleeve.
A combustor casing is attached to the end of the flow sleeve. A cap assembly is mounted inside the combustor casing. The cap assembly includes an inner sleeve that is concentrically mounted inside an outer sleeve. Both the inner and outer sleeves are generally cylindrical in configuration.
The end of the combustor liner surrounds and is coupled to the front edge of the inner sleeve of the cap assembly. Compressed air flowing in the annular space between the combustor liner and the flow sleeve passes into an annular space formed between the inner sleeve and outer sleeve of the cap assembly. The air then makes an approximately 180° turn, and the air then passes by a plurality of fuel injectors, where fuel is added to the compressed air. The air-fuel mixture passes through the inner portion of the cap assembly, inside the inner sleeve, and then out into the combustor liner, at which point the air-fuel mixture is ignited. The combustion gases then pass through the inside of the combustor liner.
Elements attached to the combustor liner and the cap assembly are used to properly position the flow sleeve and the combustor liner with respect to the cap assembly and the combustor casing. A liner stop is welded to the inner surface of the outer sleeve of the cap assembly. An end of the liner stop abuts and engages a lug which is attached to the exterior surface of the combustor liner. Abutment of the liner stop against the lug locates the end of the combustor liner and the flow sleeve with respect to the combustor casing and the cap assembly. The abutment also prevents relative rotation between these elements.
The combustor assembly described above suffers from several inefficiencies. First, the liner stop and lug are located directly in the flow path of the compressed air passing from the annular space between the combustor liner and the flow sleeve into the annular space between the inner sleeve and outer sleeve of the cap assembly. This impedes the air flow, and also introduces turbulent flow patterns around each liner stop and lug location. In addition, the liner stop and lug tend to experience wear, and they require periodic maintenance.
In addition, as the flow of compressed air passes from the annular space between the combustor liner and flow sleeve into the annular space between the inner sleeve and outer sleeve of the cap assembly, the compressed air experiences a sudden expansion. More specifically, because the outer diameter of the end of the combustor liner is greater than the outer diameter of the inner sleeve of the cap, there is a sudden expansion as the compressed air passes over the end of the combustor liner.
In addition, as the compressed air exits the cap assembly and is dumped into the plenum area within the combustor casing, the air experiences another even greater expansion.
These sudden expansions cause shearing between varying velocity air streams, and this shearing causes parasitic losses which reduce the overall efficiency of the turbine engine. The shearing that occurs as a result of these sudden expansions generate friction and heat which serve no purpose, and thus result in energy losses. Also, the heating caused by this shearing tends to reduce the density of the compressed air, which also lowers the efficiency of the turbine.